There maybe times when you might think using a genny might come in handy but to be honest most of the time if you ask me they are not required if using a 3000 watt wet vac or below.
During the site survey and quotation process it's easy to find out which is the most practical source of power for each job as well as any access issues etc. Therefore explaining to customers the most suitable method/s going to be used, option for a power source, access etc can easily be sorted beforehand before booking any work in.
If you want to be totally independent power wise then buy & cart a genny about as each to their own. Likewise if not it's no big deal as people might make out to be.